UNIT 5 PROTEIN SYNTHESIS NOTES
DNA is the molecular basis for inheritance.
Important Early Discoveries
Fred Griffith (1928) – Experiments with __________________ and bacterial transformation
determined that there is a molecule that controls __________________.
Oswald T. Avery (1944) - Transformation experiment determined that __________ was the
genetic material responsible for _________________ results (not RNA).
Hershey-Chase Experiments (1952) – discovered that DNA from ___________ can program
________________ to make new viruses.
Erwin Chargaff (1947) – noted the _____________ of A=T and G=C, and an overall regularity in
the amounts of A,T,C and G within a ______________.
Frederick Griffith’s Transformation Experiment
The ________________ of the genetic role of DNA began by Frederick Griffith in 1928. Griffith
wanted to find out what made people __________. He studied two ___________ of bacteria
that caused pneumonia:
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Smooth= deadly, rough= safe
Mice were injected with bacteria from smooth _______________ and died. Mice were also
injected with a mix of heat-killed ____________, and live rough bacteria and then died. He
concluded that the rough bacteria had ____________________ into smooth bacteria.
Oswald Avery’s Transformation Experiment
In 1944, Oswald Avery announced that the transforming _______________, first discovered by
Griffith, was DNA. Their conclusion was based on experimental evidence that _________ DNA
worked in transforming harmless bacteria into _______________ bacteria. Avery used heat and
enzymes to determine what was __________________. Transformation did not occur when DNA
was _____________________.
Hershey-Chase’s Bacteriophage Experiment
In 1952, Alfred Hershey and Martha Chase performed experiments showing that DNA is the
genetic material of a ______________ known as T2. A bacteriophage is a virus that infects a
bacteria cell. It has a protein coat and a core made of DNA. It will attached to the bacteria
and ____________ its DNA. They performed several experiments to determine that DNA was
the genetic info ______________ on, not the protein coat.
Additional Evidence that DNA is Genetic Material
In 1947, Erwin Chargaff reported that DNA _________________ varies from one species to the
next. This evidence of diversity made DNA a more credible candidate for the genetic
material. Genes were known to have three critical ________________:
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To carry genetic info from one generation to the next.
To put the genetic info to ___________ by determining heritable
characteristics.
Genes had to be _______________ copied.
By the 1950s, it was already known that DNA is a ________________ of
nucleotides, each consisting of a nitrogenous base, a sugar, and a
___________________ group.
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4 nitrogenous bases: adenine, guanine, cytosine, thymine.
Franklin’s X-ray crystallographic images of DNA enabled Watson to deduce that DNA was
_______________. The X-ray images also enabled Watson to deduce the width of the helix and
the spacing of the nitrogenous bases. The width suggested that the DNA molecule was
made up of ________ strands, forming a double helix.
Components of a Nucleotide
Backbone of phosphates and _____________. Joined randomly to form a stand of DNA:
A with T, and C with G.
James Watson & Francis Crick
1953 presented the double helix _____________ of DNA. Two primary sources of information:
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Chargaff Rule: A-T and G-C. “A strange but possibly meaningless phenomenon”.
X-ray diffraction studies by Rosalind Franklin & Maurice H. F. Wilkins, of a helix structure
with twisted strands.
Watson & Crick formulated the _______ model of DNA: a double helix of 2 strands wound
around each other.
The Structure of DNA
__________________ cells have a single circular DNA in cytoplasm; eukaryotic cells have DNA
in the nucleus in the form of ___________________. Most organisms have a different number of
chromosomes; packed together to form chromatin. Humans have over 1 meter of DNA,
_______ longer than bacteria DNA. Histones occur when DNA is coiled around _____________.
DNA is composed of four ______________, containing: adenine, cytosine, thymine, or guanine.
The amounts of A = T, G = C, and purines = pyrimidines [Chargaff’s
Rule]. Bases on _________________ strands are linked by hydrogen
bonds: A with T, and G with C.
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Purine = 2 rings hooked together, Pyrimadine = only 1 ring.
DNA is a double-stranded helix with _________________________ strands [Watson and Crick].
Nucleotides in each strand are linked. Nucleosomes help fold up DNA to fit into chromatin.
The Basic Principle: Base Pairing to a Template Strand
The relationship between _______________ and function is manifest in the double helix. Since
the two strands of DNA are ____________________ each strand acts as a template for building
a new strand in replication. In DNA replication, the parent molecule ________________, and
two new daughter strands are built based on base-pairing rules.
DNA Replication
The parent molecule unwinds, and two new __________________ strands are built based on
base-pairing rules, that are identical to original strand. Each strand serves as a template or
model. DNA must replicate during each cell division.
DNA can begin replication at ______ part of the strand.
3 _____________________ models for DNA replication
were hypothesized:
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Semiconservative replication
Conservative replication
Dispersive replication
DNA Replication is Semi-Conservative
Each 2-stranded daughter molecule is only ___________ new. One original strand was used as
a ________________ to make the new strand.
DNA Replication
Copying DNA is remarkable in its speed and accuracy. Involves unwinding the double helix
and __________________ two new strands. More than a dozen enzymes and other proteins
participate in DNA replication. The replication of a DNA molecule begins at special sites
called the replication _________, where the two strands are separated by taking the
__________________ bonds apart.
Mechanisms of DNA Replication
DNA replication is catalyzed by DNA polymerase which needs an ________ primer. DNA
polymerase cannot initiate the synthesis of a polynucleotide, they can only ________
nucleotides to the 3’ end. DNA polymerase is a “proof-reader”. The initial nucleotide strand is
an RNA primer. RNA primase synthesizes primer on DNA strand. DNA polymerase adds
___________________ to the 3’ end of the growing strand, matching the bases together.
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Ex: TACGTT with ATGCAA
The Structure of RNA
DNA and RNA differences: DNA is the ____________ genetic code, RNA only codes for
_____________. DNA is made of 2 long strands, RNA is only 1 _____________ strand. Sugar in
DNA is deoxyribose, sugar in RNA is ribose. RNA contains ______________ in place of thymine.
Types of RNA
The job of RNA is to ________________ amino acids into proteins.
There are 3 types of RNA:
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mRNA (_________________): carries copies of instructions
for assembly of amino acids to the rest of the cell.
rRNA (__________________): assembles proteins on
ribosomes, ribosomes are also made of rRNA.
tRNA (__________________): transfers each amino acid to
the ribosome to help assemble proteins.
Mechanisms of DNA Transcription
Many proteins assist in DNA replication including RNA -______________________: Uses one
strand of DNA as a template to assemble nucleotides into a single strand of RNA. Also binds
only to DNA __________________ at specific base sequences.
Replication
Helicase protein binds to DNA sequences called origins and unwinds DNA strands. Binding
proteins ________________ single strands from rewinding. Primase _____________ makes a short
segment of RNA complementary to the DNA, a primer.
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DNA polymerase enzyme adds DNA nucleotides to the RNA primer.
DNA polymerase proofreads bases added and replaces incorrect nucleotides.
Leading strand synthesis continues in a 5’ to 3’ direction.
Discontinuous synthesis produces 5’ to 3’ DNA segments called Okazaki fragments.
Exonuclease activity of DNA polymerase I removes RNA primers.
Polymerase activity of DNA polymerase I fills the gaps. Ligase forms bonds between
sugar-phosphate backbone.
Proofreading
DNA must be faithfully replicated…but mistakes occur. DNA polymerase inserts the
___________ nucleotide base in 1/10,000 bases. DNA poymerasel has a proofreading
capability and can correct errors.
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Mismatch repair: ‘wrong’ inserted base can be ______________.
Excision repair: DNA may be damaged by chemicals, radiation, etc. Mechanism to
cut out and _______________ with correct bases.
Mutations
A mismatching of base pairs, can occur at a rate of 1 per 100,000 bases. DNA polymerase
proofreads and repairs ___________________ mismatched pairs. Chances of a mutation
occurring at any one gene is over 1 in 10,000,000,000 (billion). Because the human genome is
so large, even at this rate, mutations add up. Each of us probably inherited 3-4 ____________!
Proofreading and DNA
DNA polymerases proofread newly made DNA, replacing any incorrect nucleotides. In
mismatch repair of DNA, repair enzymes correct errors in base pairing. In nucleotide excision
DNA repair nucleases cut out and replace damaged stretches of DNA.
Accuracy of DNA Replication
The chromosome of E. coli bacteria contains about 5 million bases pairs. Capable of
copying this DNA in less than an ________. The 46 chromosomes of a human cell contain
about 6 BILLION base pairs of DNA!!
Printed one letter (A,C,T,G) at a time…would fill up over 900 volumes of a book. Takes a cell
a few hours to copy this DNA. With amazing accuracy – an average of only 1 per billion
nucleotides may be incorrect.
Replicating the ends of DNA molecules
The ends of eukaryotic chromosomal DNA get ___________ with each round of replication.
Telomeres: Eukaryotic chromosomal DNA molecules have them at the ends of nucleotide
sequences, which __________________ the erosion of genes near the ends of DNA molecules.
If the chromosomes of germ cells became shorter in every cell cycle essential genes would
eventually be _______________ from the gametes(egg/sperm) they produce. An enzyme
called telomerase catalyzes the lengthening of telomeres in germ cells(keeps them long).
RNA Editing
Intron sections of eukaryotic genes are _________________ during editing in the nucleus,
while the exon sections get spliced back together. RNA molecules can be cut and spliced
in _________ different ways, in different tissues, and serve many different _______________.
Introns and exons play a role in evolution by making very small changes in the DNA
sequence over _________.
The Genetic Code
Proteins are made by joining amino acids into long ____________
called polypeptides. The 4 bases in RNA (A, U, G, C) carry
instructions for 20 different amino acids. The code is ___________
3 bases at a time, each sequence of 3 complementary bases
= 1 amino acid. There are 64 different ___________________ of
possibilities. All amino acids “start” with AUG.
Translation
Cells use info from mRNA to make proteins in the _________________. Before translation occurs,
mRNA is transcribed ________ DNA. tRNA helps bring amino acids into the __________________
to form peptide chains. When ribosome reaches a “stop” codon it __________________ the
polypeptide and mRNA into the cytoplasm.
RNA & DNA
RNA goes to and makes up the ribosomes in the cytoplasm. The proteins that RNA codes for
also serve as ____________ to help catalyze reactions. DNA is the ____________ plan/blueprints
and always stays in the nucleus. Genes are key to all the functions of living things.
Mutations
Changes in genetic material, some good and some bad:
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Point Mutations change a _____________ point in a DNA sequence.
Frameshift Mutations are caused when there is an insertion or
deletion of a ___________________.
o Insertion is an ___________ letter or two getting put in the
sequence.
o Deletion is when one or two letters are __________________ out.
Duplication an extra ___________ on part of the chromosome.
Inversion part of a chromosome gets ___________________ in
direction.
Translocation happens when part of the chromosome breaks off
and attaches to _________________ chromosome.
Point mutations affect only one nucleotide… While Frameshift mutations affect _____________
amino acid that follows the place of the mutation. Mutations that cause dramatic changes
are often _________________. Slight mutations that are not harmful are a source of
_______________ in species.
Polyploidy occurs when an organism has an extra ______ of chromosomes!
Gene Regulation
RNA Polymerase binds to the _______________ region of a DNA sequence to turn a gene on
and off. DNA-binding proteins also help to turn genes on and off. Operons are groups of
genes that work together for a ____________________ function.
Lac Operon Example
Lac operon genes are found in certain _________________ and help the
bacteria to be able to use lactose as food (lactose is a simple sugar). If
lactose is ______________ the lac operon will turn the gene on, if not, the
gene will remain off.
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Turned on by RNA Polymerase binding to a promoter.
Turned off by a Repressor Protein binding to the operon.
Repressor proteins _________ gene transcription by _______________
the DNA strand so that RNA Polymerase cannot read it. The lac operon
turns on when lactose is present because the DNA strand will
_________________, causing the repressor protein to fall off. Now RNA
polymerase can attach to the promotor.
Gene Regulation
Many other different types of genes are regulated by repressor proteins. Some genes even
use proteins to ________________ the rate of transcription. ______________ are only found in
bacteria cells. Eukaryotic cells genes are controlled ___________________ by complex
regulatory sequences.
TATA Box
TATA box is a place in the eukaryotic gene sequence that helps _____________ where RNA
polymerase needs to begin transcription. Promoters are short DNA sequences found just
_______________ the TATA box.
Gene Expression
Proteins that bind to enhancer sequences of a gene can work to ________________ gene
expression by:
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Many proteins can bind to ____________________ enhancer sequences.
Some enhance transcription by opening up ________________ coiled chromatin.
Help attract RNA polymerase.
Eukaryotes vs. Prokaryotes
Gene regulation in eukaryotes is more _________________ than in prokaryotes. Cell
specialization requires genetic _______________________ . All eukaryotic cells carry the
____________ genetic code; each type of cell performs a different function in a different part
of the body.
Development and Differentiation
Hox genes control the differentiation of cells and tissues of ____________________ embryos.
Animals share many common __________________ of development because we all share the
same bases (ATGC) but have different numbers and _____________________ of chromosomes.
Fruit flies can grow legs on their head if the hox gene is tampered with during development.
In humans the hox gene acts similar to fruit fly’s.